In accordance with an established lining process, for pipelines or passageways which are located underground, a flexible tubular liner is everted into the passageway using a liquid to evert the liner. The liner is held to the pipeline or passageway shape whilst synthetic resin which impregnates an absorbent layer of the liner is cured, whereby the pipeline or passageway is lined with what in effect is a rigid lining. This method has proved to be extremely successful, but does suffer from the disadvantage that the lining also extends across side connection apertures whereby side connecting or lateral pipes which previously led into the underground pipeline or passageway, become blocked. They must be re-opened, and the present invention is concerned with a cutter for performing this re-opening of the lateral or side connecting pipes.
The aforesaid lining process has found wide application in the lining of underground sewer pipes and passageways. Lateral connecting pipes to underground sewers, pipes or passageways typically will lead from domestic dwellings or other premises, and it is therefore easily understood that the connections between the sewer and the side connections or laterals must be re-established as soon as possible, and must also be established in an efficient manner, whereby the connecting aperture after lining and cutting is not substantially smaller than the original connecting aperture before lining.
As can be appreciated, various cutting devices have already been proposed, a typical one of which is disclosed in the U.S. Pat. No. 4,197,908. The known cutting devices are provided with a rotary cutter bit which is rotated about an axis which is substantially radial with respect to the pipe in which it operates. The cutter bit is adapted to be moved in an angular fashion about an axis which is longitudinal of the pipe, and also can be moved longitudinally of the pipe. Thirdly, the cutter bit can move radially outwards and inwards. These various movements are provided to enable the cutter bit to follow the contour of the opening which is covered by the lining material, to ensure the effective re-establishment of the connection between the lateral and main pipe. The radial movement of the cutter is related only to the depth of penetration of the cutter bit, and therefore the means enabling the cutter bit to follow the contour of the opening comprises the two motions being the angular adjustment of the cutter bit about the axis extending longitudinally of the pipe, and the longitudinal movement of the cutter bit. This control of the cutter movement is bound to have significant disadvantages in that the cutter bit axis, during the following of the said contour, varies with respect to the direction in which the lateral or side connecting pipe meets the main passageway, with the result that there can remain "ledges" of lining material overlapping the original opening size, and such ledges are a means for trapping debris and waste material to the detriment of the efficiency of the connection with the main passage, and in some cases leading to the eventual obstruction of the passage by blockage.